DNA which has the capacity to code for polypeptides, can be synthesized and spliced into plasmid DNA and then when cells are transformed by this recombinant DNA, the synthetic DNA will replicate in these cells. If properly inserted in phase with a suitable bacterial promoter, the synthetic DNA will be decoded (expressed) into the authentic polypeptide. The technique can be used for the production of various hormones, enzymes and other polypeptides. In each case the technique has to be adapted to the specific circumstances.